The present invention relates to a valve driving apparatus provided in an internal combustion engine. Especially, the valve driving apparatus drives an exhaust valve by using an electromagnetic force, and it is appropriate for the exhaust valve to function to be movable between an open and a closed position.
A valve driving apparatus which drives an exhaust valve by using electromagnetic force is already known, as disclosed in Japanese Laid-Open Patent Application No. 10-18819 or No. 10-18820. An armature is coupled with an electromagnetic valve (or called exhaust valve) which is provided in this valve driving apparatus. On the upper side of the armature, the first electromagnet and an upper spring are deposited, and on the lower side of the armature, the second electromagnet and a lower spring are deposited. The armature is held at the neutral position in the middle between the first and second electromagnets by the forces of the upper and lower springs. The electromagnetic valve is full closed when the armature touches the first electromagnet, and the electromagnetic valve is full open when the armature touches the second electromagnet. In the above-mentioned valve driving apparatus, the exhaust valve is held at the full closed position by the fact that a predetermined exciting current is supplied to the first electromagnet and the armature is attracted by the first electromagnet. When the supply of the exciting current to the first electromagnet is cut, the armature is pushed by the upper spring and the exhaust valve begins to move in the opening direction. If a predetermined exciting current is supplied to the second electromagnet when the exhaust valve is positioned at a predetermined position, a damping of displacement amplitude by friction of the exhaust valve or remaining pressure of combustion is supplemented and the exhaust valve reaches the full open position by the fact that the electromagnetic force is supplied to the armature in the opening direction.
If the exhaust valve is moving at a high speed when the exhaust valve arrives at the full open position, that is, the armature touches the second electromagnet, such problems as increasing of activating noise of the exhaust valve or bouncing back of the exhaust valve occur. Therefore, in the aforementioned valve driving apparatus, the speed of the exhaust valve is restrained when the exhaust valve approaches to the full open position, by reducing the exciting current to the second electromagnet when the exhaust valve reaches near the full open position.
Incidentally, in the internal combustion engine installed on a vehicle, when an accelerator pedal is disengaged during the high speed driving, for example, a fuel injection cut control for stopping a fuel injection to a combustion chamber of the engine is executed. Because combustion does not occur in the process of the fuel injection cut control, the pressure in the combustion chamber of the engine is negative (or called vacuum) when the exhaust valve is at the opening timing, that is, a piston of the engine is near bottom dead center. This negative pressure forces the exhaust valve in the opening direction. Consequently, if the same value of the exciting current is supplied to the second electromagnet in the execution of the fuel injection cut control, the armature touches the second electromagnet at the higher speed. Consumed electric energy increases, because it is necessary to supply the exciting current again to pull the armature back to the second electromagnet in order to prevent the armature from bouncing back. Furthermore, a large noise occurs by the high speed collision between the armature and the second electromagnet.
It is thus one object of the present invention to solve the aforementioned problems. The present invention provides a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is movable between an open position and a closed position. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a control means. The control means controls the electromagnetic force applied to the armature in the direction of the closed position of the exhaust valve when the exhaust valve is moving to open, in the case that combustion is suspended because of a fuel injection cut control in the internal combustion engine.
This control means supplies the electromagnetic force to the armature coupled with the exhaust valve in the direction of the closed position, when the exhaust valve is moving to the open position, in the case that combustion does not occur in the engine. When combustion is suspended in the engine, negative pressure is generated in the combustion chamber of the engine at the timing near the bottom dead center which is the opening timing of the exhaust valve. The force applied to the exhaust valve by the negative pressure is canceled by the electromagnetic force in the direction of the closed position applied to the armature by the control means. Consequently, the armature is prevented from colliding with the electromagnet at high speed. Therefore, the armature does not bounce back from the electromagnet, and the activating noise of the exhaust valve can be restrained. When combustion is suspended in the fuel injection cut control, an engine brake occurs on the basis of the negative pressure of the combustion chamber. Then, the engine brake is obtained securely by the present invention.
The above-mentioned object is achieved by another embodiment of the present invention. That embodiment is also a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is movable between an open position and a closed position, in the same way as depicted in the first embodiment. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a valve timing changing means. The valve timing changing means changes an opening timing of the exhaust valve, in the case that combustion is suspended in the internal combustion engine.
Generally speaking, the combustion chamber pressure is negative near the bottom dead center which is the opening timing of the exhaust valve, when combustion is suspended in the engine. However, since the valve timing changing means in this embodiment changes an opening timing (advanced or delayed) of the exhaust valve, when combustion is suspended in the engine, the pressure in the combustion chamber is restrained low negative (that is, near zero), or becomes positive. Consequently, the armature does not collide with the electromagnet at high speed. Therefore, it prevents the armature from bouncing back from the electromagnet, and the activating noise of the exhaust valve can be restrained. Since extra electromagnetic force to the armature is not necessary, electric power can be saved.
The above-mentioned object is also achieved by another embodiment of the present invention. That embodiment is also a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is also movable between an open position and a closed position. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a reducing control means. The reducing control means controls the electromagnetic force applied to the armature in the direction of the open position of the exhaust valve when combustion is suspended in the engine less than when combustion is underway in the engine.
Since the electromagnetic reducing means controls the electromagnetic force on the armature in the direction of the open position of the exhaust valve when combustion is suspended in the engine less than when combustion is underway in the engine, the electromagnetic force in the direction of the open position of the exhaust valve is reduced. Consequently, the armature does not collide against the electromagnet at high speed. Therefore, the armature does not bounce back from the electromagnet, and the activating noise of the exhaust valve can be restrained. Since extra electromagnetic force to the armature is not necessary, electric power can be saved. Furthermore, since the combustion chamber pressure in the engine is negative, therefore the engine brake can be secured.
Furthermore, the above-mentioned object is also achieved by another embodiment of the present invention. That embodiment is also a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is also movable between an open position and a closed position. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a suspending means. The suspending means suspends a moving of the exhaust valve when combustion is suspended in the engine.
Since the suspending means suspends a moving of the exhaust valve when combustion is suspended in the engine, the armature coupled with the exhaust valve does not collide against a magnet at high speed. Moreover, an exciting current to the electromagnetic coil for attracting the armature can be reduced, therefore saving of an electric power can be attained.